The present invention relates to an improved imaging material of the type employing microcapsules containing a photosensitive composition. More particularly, it relates to imaging materials in which the photosensitive composition contains a photoinitiator system which includes an absorber, a coinitiator, and autoxidizer to provide improved film speed.
Imaging systems employing photosensitive microcapsules are described in commonly assigned U.S. Pat. Nos. 4,399,209 and 4,440,836 and commonly assigned U.S. applications Ser. No. 339,917 filed January 18, 1982, and Ser. No. 620,994 filed June 15, 1984. The imaging systems, in their simplest form, comprise an imaging sheet having a layer of photosensitive microcapsules coated on one surface. The internal phase of the microcapsules includes a photosensitive composition and, more typically, a photocurable composition which cures by free radical addition polymerization. In the most typical embodiments, the internal phase also includes an image-forming agent such as a substantially colorless electron donating color former.
Images are formed using the aforementioned systems by image-wise exposing the layer of microcapsules to actinic radiation and subjecting the layer to a uniform rupturing force in the presence of a developer material. U.S. Pat. No. 4,399,209 discloses a transfer imaging system in which the developer material is provided on a support which is separate and distinct from the imaging sheet. After exposing the imaging sheet, it is assembled with the developer carrying sheet and the two are passed together between a pair of pressure rollers with their reactive faces in contact. U.S. Pat. No. 4,440,846 describes a self-contained system in which the developer is provided on the same surface of the support as the photosensitive microcapsules. Upon rupturing the microcapsules, the color former is image-wise released and reacts with the developer to provide a color image.
U.S. applications Ser. Nos. 339,917 and 620,994 describe full color imaging systems in which three sets of microcapsules respectively containing cyan, magenta and yellow color formers are provided on one or separate supports and image-wise exposed using color separation techniques. In one embodiment, the three sets of the microcapsules have distinct sensitivities such that they can be mixed and exposed on the surface of a single support.
While the imaging systems and photosensitive microcapsules described in the aforementioned patents and patent applications are useful in forming images, there is a need for higher film speeds than have previously been achieved.